Linear tape drive systems provide for high-density recording on multiple tracks of a magnetic storage tape. In certain arrangements, parallel tracks extend along a longitudinal direction of the tape. During recording or playback, the read/write elements of the head should be aligned with the desired track as the tape moves in a longitudinal direction across the head. Closed loop positioners are often used in tape systems having higher track densities. In high-density tape systems, the tape may wander in the lateral direction (perpendicular to the longitudinal direction) as it moves in the longitudinal direction across the head, which can result in a positioning error or offset between the head and a center line of the desired track. Moreover, if the positioning error or offset is sufficiently large, it can further result in a track misregistration (TMR) error.
To avoid these types of problems, tape cartridges for high-density tape drives are preformatted with what is known as servo information, which is used to maintain the correct lateral position of the tape with respect to the read/write head. Servo information provides the system with feedback that is used to continuously position the head relative to the tape. Analysis of the servo signals such as a position error signal (“PES”) allows for a determination of an offset and the distance of the offset between the track and the head. Based on the PES, the head is moved by a positioner in the lateral direction to the center line of the track so that write/read operations can occur properly.
Linear Tape Open (“LTO”) is a computer storage magnetic tape format that employs a servo-based, closed loop control mechanism. The LTO roadmap calls for successive increases in capacity and speed, requiring increased track densities. As track densities increase with each new generation of LTO tape cartridges, the ability to precisely control the read/write head relative to the magnetic tape becomes increasingly important and more difficult. External vibrations (also sometimes referred to herein as “system disturbances”) degrade the performance of LTO drives by causing a misalignment of the head that increases the PES, thus degrading the ability of the head to follow the desired track. If the tracking performance degrades too far then a TMR error can occur causing the drive to stop reading or writing.
Because external vibrations are present in most non-sterile conditions (due to fans, hard drives, and other rotating systems), it is imperative to compensate for such external vibrations to decrease the likelihood and/or extent of TMR. Previous technology uses an additional sensor such as an accelerometer to measure the external vibrations and feed forward the signal, possibly through a filter, to control the position of the head. Unfortunately, such technology has certain limitations. A critical element of this previous technology is the ability to measure the external vibrations ahead (in time) of when they affect the position of the head. Due to imperfections in the sensor, additional filtering is required in order to increase accuracy. As a result, incorporating a sensor into the system can increase the overall complexity of the drive.